Production of cast iron



Patented Aug. 8, 1944 UNITED STATES "PATENT, OFFICE PRODUCTION OF CASTIRON John T. Eash, Westfield, N. 1., as signor to The InternationalNickel Company, Inc., New York, N. Y., a corporation of Delaware NoDrawing. Application October 14, 1943, Serial No. 506,262

11 Claims coma-13o) The present invention relates to an addition alloyand more particularly to an addition alloy for use in producing castiron.

Cast irons containing low carbon and/or sili-- con for the section sizeinvolved and/or containing appreciable amounts of carbide stabilizingelements and cast irons produced under conditions of rapid freezing tendto becomeance to scufling. The cast iron may exhibit the dendriticstructure near the surface and some distance below the surface or mayexhibit the dendritic structure throughout the entire cross section. Thedendritie graphite structure also tends to result in poor machinability,strength and toughness and low growth resistance, etc. The production ofmachinetools, gears, automotive and engine castings, cylinder heads,cylinders, pistons, piston rings, pumps, valves, etc, has presentedparticular problems. The production of cast iron piston rings, which aremade of, relatively high carboncast iron but are cast in rather smallsection sizes, illustrates some of the defects and problems encounteredin the production of cast iron products. The production of piston ringsis but one of the many examples that could be cited. Piston rings,especially for airplane engines, must-possess a special combination ofproperties. They must possess high mechanical properties and mustexhibit resistance to scuffing properties in order to obtainsatisfactory wear resistance. Furthermore as the piston ring blanks arecast individually and then machined to proper size it is essential thatthey possess adequate machinability and be substantially free from hardspots which interfere with machining and which rapidly decrease the lifeof the cutting tool. In producing the rough piston rings, i. e., thepiston ring blanks, it is im-- vantages connected with the use of priorinoc-- portant that the method employed yield a product having thedesired hardness and that it neither raise nor lower the hardnessexcessively. Methods for producing piston rings have possessed thedisadvantage of tending to produce hard spots, internal defects, pnholes, internal slag particles, white edges, low strength, excessivelydecreased hardness, an fopen iron, dendritic graphite, substantialamounts of primary or fine ferrite associated with dendritic graphite,low scuffing resistance, and/or other disadvantages. In some proposedmethods various 1noculants and addition alloys were used but it wasfound that in overcoming one defect these inoculants and addition alloysproduced another defect or shortcoming. Thus, treating the relativelyhigh carbon cast iron used for piston rings with an addition offerro-silicon in sufilcient amounts. to produce an inoculating effecttended to produce kish on the melt and to yield an open iron havingexcessively reduced hardness. Calcium silicide additions had a similareffect. Additions of an alloy. containing about 6% silicon and 92%nickel in amounts sufficientto have an inoculating effect raised thehardness excessively. Additions in quantities sufiicient to completelyinoculate cast iron. i. e., in quantities suflicient to secure theproper graphite structure, of an alloy containing about 20% silicon, 33%chromium, 15% manganese,

2.5% carbon, 1% calcium and balance iron, or an alloy containing about25% to 50% chromium, 10% to 25% silicon, 5% to 15% manganese, 0.2% to 2%or more calcium, often with about 0.2% to 2% titanium, and balance ,ironplus small amounts of minor constituents such as carbon, etc., e. g., analloy containing about 40% chromium, 15% silicon, 10% manganese, 1%titanium, 0.5% calcium and balance iron, tended to produce white edges.about 755% silicon, 7.5% manganese, 7% Znconium, 0.5% aluminum, andbalance iron tended to produce pin holes and internal slag particles andyielded a piston ring having lower hardness than desired. An additionagent of silicon and graphite produced kish on the melt and yielded aproduct having lower hardness than desired. Additions of term-siliconcontaining aluminum had the same effect and also tended to produce pinholes. Because of the disadulants and addition alloys, most'commercialproducers of piston rings avoided the use of any inoculant or ladleaddition alloy. The commercial methods used to produce piston ringssuffered from the disadvantage that inconsistent results were obtained.Sometimes the method yielded good results and at other times yieldedunsatisfactory results, for example, hard spots, dendritic graphite,fine free ferrite, etc. Generally, un-

satisfactory results were associated with a den- 'dritic., structure. Inorder to minimize these defects, some piston rings have been chromium-An' alloy containing plated. In actual tests conducted on commerciallyproduced machined piston rings, it was trusion. The galling is oftenevidenced by deep pitting and scoring.

- The foregoing illustrates, by reference to the production of cast ironpiston rings, some of the. defects and problems encountered in producingcast iron products. The production of machine tool beds and frames orautomotive and engine castings, including pistons, cylinders, cylinderheads, cylinder blocks, etc., or high strength gears or pumps or valvesor numerous other cast ironproducts likewise exhibited various defectsand difficulties which are overcome by the invention describedhereinafter. It is to be understood that the present invention is notlimited to the illustrative examples cited herein butv is broadlyapplicable to the treatment of cast iron to improve the properties ofthe product. Thus, machine tool beds made of cast iron produced withouta late addition of an alloy-tendedto have hard spots which detrimentallyaffected the machining of the beds and tended to have a detrimentaldendritic graphite structure, usually in association with fine freeferrite, which resulted in scufiing and galling on the wearing surfacewhere the cast iron was subjected to sliding contact with another metalpart. Such a cast iron may contain about 3% carbon and 2% silicon. Thedefects encountered. in the production of machine tool beds and othercast iron products have been recognized and discussed in the literature,

for example in F. J. Dost's article on Making better machine toolcastings" published in Mechanical Engineering, May, 1940, pages 365 etseq. and the discussion of said article published in MechanicalEngineering, March, 1941, pages 226 to 229.

As another example, the production of a Diesel engine piston, havingring grooves chilled to eliminate leakage, resulted in an unmachinableproduct when produced without a late addition of an .not detrimentallyaffect the strength and other desired properties. Attempts to produce ama- .chinable chilled groove piston having high strength by additions ofprior known alloys were not satisfactory. Thus, late additions offerrosilicon did not reduce the chill sufliciently to consistently yielda machinable piston. Sometimes the cast iron was machinable andsometimes it was not machinable, although in both instances the castironv might. have the same hardness. Late additions of an alloycontaining about 6% silicon and balance mainly nickel, or of an alloyfalling within the range of about 25% to chromium, 10% to 25% silicon,5% to 15% manganese, 0.2% to 2% calcium, often also containing about0.2% to 2% titanium, and balance mainly iron, likewise did not reducethe chill sufficiently. A late addition of an alloy containing about 75%silicon, 7.5% manganese, 7% zirconium, 0.5% aluminum and balance ironreduced the chill but at the same time markedly reduced the strength ofthe cast iron compared to those treated by the previously mentionedalloys. Furthermore, the use of ferro-silicon produced a product whichtended to exhibit pin holes or gas holes. Additions of the alloycontaining 75% silicon, 7.5% manganese, 7% zirconium, 0.5% aluminum andbalance iron had a similar effect and, in addition, tended to result inscumming. In view of the shortcomings of the prior addition alloys, ademand existed for a suitable alloy to be used as a late addition inproducing cast iron pistons. A suitable cast iron .for pistons mightcontain about 2.9% to 3.3% carbon, 1.6% to 2.2% silicon, 0.9% to 1.8%nickel, and 0.5% to 0.8% molybdenum.

The foregoing examples also illustrate some of the defects and/orshortcomings of prior known alloys when used as a late addition to castiron. These prior alloys possess various undesirable features such ascausing hardening, or alternatively, excessive softening and weakeningor decreased strength. Scumming, pin-holing, hard spots, white edges,and/or the production of kish, are some of the other defects associatedwith the use of prior alloys.

Many of the commonly used inoculants and addition alloys had highmelting points which were also undesirable characteristics. For example,the 50% grade of ferro-silicon melts at about 2250 F.; the 85% grade offerro-silicon melts at about 2450 FL; silicon carbide melts above 2600F.; and commercial calcium silicide melts at about 2100 F. Theseinoculants and addition alloys, particularly calcium silicide, do nothave as high a solution rate in the molten iron as desired.

I have discovered that the foregoing and other difiiculties may beavoided and that high quality cast iron can be produced consistently bya simple and efficient method involving the use of a novel additionalloy that produces an inoculating effect on cast iron.

It is an object of the present invention to provide a novel additionalloy.

It is another object of the invention to provide a novelladle additionalloy containing special proportions of nickel, silicon and calciumwhich is particularly suitable for producing high quality cast iron.

It is a further object of the invention to provide a method ofconsistently producing cast iron having high mechanical properties andsubstantially free from the defects normally associated with the use ofprior art inoculants and addition alloys, said process involving the useof a novel addition alloy.

Th invention also contemplates a method of consistently controlling themicrostructure of cast iron to obtain a structure substantially devoidof areas'containing fine dendritic graphite associated with fine freeferrite, said method involv ing the use of a novel addition alloy.

Other objects and advantages of the invention will become apparent tothose skilled in the art from the following description.

The present invention provides novel alloys particularly'adapted for useas addition alloys to cast iron and the like for reducing chill andproducing random graphite distribution without detrimenproperties. Thealloys provided by the invention ass-5,059

contain about 27% to 50% silicon, a small but effective amount, say0.07%, to 1% calcium, a small amount-up to 20% iron and the balancesubstantially all nickel. In general, the composition of the alloys willfall within the ranges set forth in Table I.

a of about 34% to about 67%.

Table I y Element Range Percent silicon 21 to 60 Percent calcium e 0.1to 1 Percent iron. 6 to 20 Percent nickel Balance The nickelcontent willfall within the ranges It is essential that the nickel and siliconcontents be maintained within the foregoing proportions in order thatthe desired combination of properties of the alloy be obtained. If thesilicon content is not sufllciently high the melting, point of the alloyis high and solution in the molten iron is impeded. If the silicon islow the alloys do not have as effective chill reducing tendencies aswith the optimum silicon content. When the silicon content is above thestated range, the melting point is raised again, with attendantdifliculties, and maximum strength values in the resulting cast iron arenot obtained. With the alloys pro-. vided by the present invention thereis obtained an optimum or improved balance between proper graphitizingeffect and pearlite strenthening effect. When the nickel and siliconcontents are unbalanced, i. e., are outside the balanced ranges setforth hereinbefore, the alloy has decreased mobility, fluidity andactivity. The calcium content in combination with balanced nickel andsilicon contents are essential in order to impart consistent andeffective inoculating power to the alloy. The effect of the small amountof calcium is not completely understood but it is thought that it mayactas a catalytic agent or act in some other manner since calcium itselfapparently is not a powerful graphitizer in the small quantity involvedin the present alloy. Whatever may be the eifect of calcium, .it hasbeen found that calcium is an essential element in the presentinvention. The minimum amount,

.of calcium which will produce the desired results is about 0.07% but inorder to obtain consistent results and to allow for losses in preparingthe sidered to be the safe minimum. Thus when 1%,0! an alloy containingabout 34% silicon with nickel in the proper balanced proportion butcontaining only about 0.002% calcium was added to a cast iron containing2.2% carbon, 2.3% silicon and 0.7% manganese, the properties obtained inthe cast ironwere much inferior to those obtained when a similar alloycontaining about 0.29% calcium was added to the same cast iron. The castiron treated with the alloy containing only 0.002% calcium had a ironwas 37,800 pounds per square inch whereas the tensile strength of thelatter cast iron was 60,800 pounds per square inch. The Izod impactstrength of the former was 14 foot pounds whereas the latter had animpact strength of 31 foot pounds. Again,.the former sustained atransver'se load of 3080 pounds with a transverse deflection of 0.089inch whereas the latter cast iron sustained a transverse load of 5175pounds and had a transverse deflection of 0.160 inch.

The addition alloy for cast iron provided by the invention possesses alow melting point, high mobility, the property of being rapidlyassimilated, the power to exert a positive and profound efl'ectinforcing the precipitation of graphite to occur at a higher temperature,the power to eliminate the presence of fine ferrite residues and theproperty of reducing chill. These properties must' be achieved by thesimultaneous addition of the essential ingredients in a single alloyrather than through the separate addition of the individual constituentsor parts of them. Thus, the addition of term-silicone. g., ferro-siliconcontaining about 85% silicon, did not give as consistent resuits. anddid not produce as high transverse and impact properties as obtained byadding the improved alloy. Furthermore, the cast iron is not assensitive to excessive additions of the improved alloy as it is toexcess ferro-silicon. Excesses oilv the improved alloy stabilize thepearlite whereas excesses of ferro-silicon cause the formation offerrite. Likewise the addition of nickel and of ferro-silicon, e. g.,about 0.7% nickel and 0.4% of the 85% grade of ferro-silicon, did notgive the consistent results obtained by adding an alloy having thebalanced composition set forth herein, e. g., about 1% of an alloycontaining about 35% silicon, 0.3% calcium, and the balance mainiynickel and a small amount of iron. Also addition of the improved alloygives superior reduction in chill and high strength and impactproperties. Again, the addition of calcium silicide in amountssuflicient to introduce in the cast iron the same amount of calcium asintroduced with the improved alloy did not produce a cast iron having ashigh strength or as greatlyreduced chill as was possessed by the castiron treated with the improved alloy. Thus, in one instance, theintroduction of 0.003% calcium as a calcium-silicon V alloy about 0.1%or 0.2% is more preferably conalloy, i. e., calcium-siiicide, containingabout 32% calcium and about 68% silicon to a cast iron having a basecomposition of 2.25% total carbon and 2.25% silicon produced a cast ironhaving a total chill depth of 1.7 inches, a' clear white chill depth of0.31 inch, and 'a tensile strength of 46,800 pounds per square inch. Theaddition of the same amount of calcium in the form of the improvedaddition alloys to the same base cast iron produced cast irons havingtotal chill depths of 0.03 to 0.09 inch,,'clear white chill'depths of0.02

' to 0.07 inch and tensile strengths of 57,500 to 60,800 pounds persquareinch. A cast iron produced by adding 0.1% of: calcium as calciumsilicide gave a product having a tensile strength of 44,000 pounds persquare inch whereas the addition of 0.003% calcium in the form of theimproved alloy resulted in a product having a tensile strength of 60,000pounds persquare inch. The addition of an alloy containing about 72%silicon and balance mainly nickel or of a similar alloy containing aboutsilicon yielded a cast iron having infen'or strength compared with acast iron produced by adding the improved balanced alloy of theinvention. I

Incarrying the invention into practice it is 1 preferred to maintain thesilicon, iron and nickel contents of the addition 'alloy within theranges of about'27% -to 41% silicon, about 7% to 15% iron and about 50%to 65% nickel. An addition alloy falling within this range comprisesabout 38% silicon, 0.5% calcium, iron and 52% dental elements and minorconstituents may be present in small amounts suchas occur in commercialpractice or'in amounts not adversely affeoting the-desired properties.Usually the sum of the incidental elements will not exceed about 1% andthe amount of any one element usually will not exceed about 0.25%. Thus,some of the alloys produced in accordance with the invention havecontained 0.07% aluminum and/or 0.07% zirconium and/or 0.02% titaniumand/or 0.01% to 0.2% carbon, etc. It is to be understood that when it isstated herein that the balance of the alloy is nickel or issubstantially all nickel it is not intended to exclude amounts ofincidental elements and minor constituents such as indicated herein oras occur in commercial practice or which will not adversely affect thedesired properties. The examples set forth in Table II are illustrativeof compositions within the scope of the present invention.

Table II Percent Percent Percent Percent Si Fe Ca Ni Some of theimprovements in mechanical properties resulting from use of the additionalloys provided by the invention are illustrated in the followingexamples.

Example I Both portions of the melt were cast into arbitration barshaving a diameter of 1.2 inches and-into blocks having dimensions of 1inch by 5 inches by 4 inches. The blocks were chilled on the 1 inch by 5inch face. The untreated iron had a hard mottled structure and wasunmachinable. This untreated cast iron had'a total chill depth of 4inches and a white chilled depth of 4 inches. The iron treated inaccordance with the present invention had a relatively soft graymachinable structure and had a tensile strength of about 57,500 poundsper square inch. The treated cast iron had a total chill depth of 0.09inch and a white chill depth of 0.07 inch.

Example 11 A melt of cast iron containing about 2.25%

carbon, 2.25% silicon and 0.9% manganese was established and thensuperheated to about 2930 F. Part of the melt was cast in an untreatedcondition and part was treated with about 1% of alloy similar incomposition to those set forth in Table II and then was cast. Bothportions were cast into arbitration bars and into blocks 1 inch by 5inches by 4 inches, the 1 inch by 5 inch face being chilled. Thecomparative properties of the untreated and treated cast irons are I12-inch span.

The more sensitive properties indicative of the improvements obtained bytreatment in accordance with the invention are the decreased chillingcapacity and the increased transverse strength and deflection.

The invention provides an addition alloy, and a method involving a lateaddition of said alloy, which when used in producing cast iron enablesone to consistently control the microstructure of cast iron to obtain astructure substantially devoid of areas containing fine dentriticgraphite usually associated with fine free ferrite. This feature of thepresent alloys is particularly advantageous where it is desired toincrease the wear resistance and to decrease any tendency of the castiron to gall and to scuff.

The alloy provided by the invention hasa melting point under about 1900F., e. g., about 1800 F., which is considerably lower than that of thecommonly used addition alloys and inoculants. Furthermore the alloypossesses a high solution rate in molten iron which contributes toobtaining consistent results, The alloy is further characterized by thefact that it is substantially free from tendencies to form undesirableslag.

The invention provides a method of producing improved cast iron whichcomprises establishing a melt of cast iron, incorporating into the meltthe addition alloy provided by the invention, and casting the treatedmelt. In general, it has been found desirable to cast the melt shortlyafter the addition of the alloy. For example, a body of metal weighingup to 1000 pounds will be poured within about 1 to 15 minutes after thealloy addition. However, a large ladle of metal, e. g., 5 tons or over,may stand 30 minutes to an hour and a half before being poured. Ingeneral, the time between the addition of the alloy and pouring may varyfrom one minute to one and a half hours, depending on the size of thebody of metal being poured, its tapping temperature and the desiredpouring temperature. Usually the melt should be poured at a temperatureof at least 2550 F., preferably at least 2600 F. However,

the mold material may limit the maximum pouring temperature and when thetemperature of the melt is high may require that the treated andovercomes the shortcomings of untreated or 2%. 'The alloy may be addedin the furnace I or in the ladle in lump form or in crushed form but ispreferably added to the melt in a ladle just prior to casting and ispreferably added in a crushed form. I In carrying outthe presentinvention the amount of silicon introduced with the addition alloyshould be taken into consideration in'determining the proper siliconcontent of the melt before addition of the alloy in order to arrive atthe desired final silicon content. The

amount of silicon in the alloy introduced into' is characterized byrandomly distributed graphite,

as distinguished from dendritic graphite, and by a freedom frompulverulent ferrite, and possesses unimpaired or increased tensilestrength, transverse strength, deflection, toughness, density, wearresistance, growth resistance, etc.-, while avoiding excessive increasesor decreases in hardness and avoiding other shortcomings resulting fromthe use of prior art addition alloys or inoculants, such as hard spots,internal defects, pin holes, white edges and corners, an open. iron,formation of klsh on the melt, etc. The balanced composition of thealloy promotes the inoculation reaction, prevents the formation of adendritic graphite structure and, in addition, tends also to prevent theformation of primary or fine free ferrite associated with the dendriticgraphite as distinguished from secondary or more massive well scatteredfree ferrite. The use of the alloy in producing cast iron providescastings which. possess greater density as observed by X-ray inspection.The tendency to produce hard spots is substantially eliminated thusproviding castings with improved machinability. After adding the alloyprovided by the invention the surface of the melt is clean and is notcovered with undesirable oxide, as frequently is the case for someinoculants. By using the alloyof the invention, the desired effects canbe produced without greatly increasing the silicon content of the molteniron thereby providing wider latitude of use in different cast ironmixtures. The alloy also permits a greater latitude of compositions tosecure the desired properties than do some prior alloys.

In carrying the invention into practice it has been found that theadvantages of the alloy provided by the present invention over additionalloys and inoculants used heretofore are particularly outstanding whenused in the production of the lower carbon content irons. Thus, anaddition of about 1% of the addition alloy contemplated by the inventionnot only produced randomly distributed graphite in a low carbon ironcontaining about 2.25% total carbon and 2.25% silicon, but also raisedthe tensile strength over 20,000 pounds per square inch to produce astrength of abo t 68,000 pounds per square inch. This is a desirableadvantage as the lower carbon content cast irons sufier particularlyfrom the tendency to form an undesirable dendritic structure, especiallyin the general vicinity of the surface.

, In treating the higher carbon content cast irons, the alloy of thepresent invention also possesses advantages. It avoids the shortcomingswhich accompanied the use of prior alloys in higher carbon cast irons.

Thus, in producing cast iron piston rings a product is obtained havingrandomly dispersed graphite instead of a detrimental dendritic graphite,without the shortcomings of producing kish on the molten metal or ofproducing a. cast product having excessivelyreduced or increasedhardness, or hard spots, pin

holes, slag inclusions, internal defects; chilled edges, etc. Freedomfrom dendritic graphite and from hard spots are particularly importantin producing piston rings and other cast iron products where optimum orhigh properties and machinability are desired. For example, the presenceof a dendritic graphite structure in piston rings produced according toprior practice is a frequent occurrence and causes scuiling to such anundesirable extent that during the breakingin period, before the enginecan be placed into actual use for the intended purpose, the rings nolonger perform properly. Again, by way of example, the presence of hardspots is also a common occurrence in plston'rings and causes machiningdiiliculties, not only by impairing the tools and markedly reducingtheir life, but by within the range of about 3.25% to 4.1% carbon andabout 2.2% to 3.1% silicon. More preferred ranges comprise about 3.65%to 3.95% carbon and 2.3% to 3.0% silicon, e. g., about 3.75% carbon and2.75% silicon. The silicon content includes the amount introducediby'the addition alloy.

- As pointedout hereinbefore, chromium-plating amounts sumcient toobtain inoculating effects of piston rings has been used in order toovercome their shortcomings and incosistent properties. It is believedthat it will not be necessary to chromium-plate piston rings produced inaccordance with the present invention in,view of their consistently goodproperties and structure and their freedom from defects. The use of thepresent invention in the production of piston rings markedly reduces theloss due to rejections. For example, the loss of one producer of pistonrings was reduced from the prior high figure of over about 30%rejections to a new low figure of under. about 3% rejections. Pistonrings produced as set forth herein possess markedly reducedusceptibility to scumng, longer operating life, improved density andimproved tensile strength compared to the properties of chine tool bedor frame results in the production of a product substantially free fromhard spots, deleterious dendritic graphite and fine free ferrite whichis iisuau associated with dendritic graphite. Such a machine tool bed orframe is machinable and exhibits, good wear resistance and ,lessscuffing andgalling than beds or frames having a dendritic graphitestructure in association with fine free ferrite.

The use of the present alloys in producing cast iron pistons, forexample, Diesel engine pistons having chilled grooves, results intheconsistent production'of a product which is machinable and which doesnot suffer from impaired strength;

pin holes, and/or the other shortcomings encountered in cast ironproduced with prior known alloys. Thus, in producing a cast ironcontaining about 3.15% carbon, 1.75% silicon, 1% nickel, 0.75%molybdenum and 0.15% chromium for chilled grooved-Diesel engine pistons,a late addition of about 1% of the improved alloys resulted in theproduction of a machinable cast iron havinga tensile strength of about62,000 pounds per square inch with a chill depth of only about /32 inchon a test chilled block. When a late addition of about 1%0f an alloycontaining approximately 25% to 50% chromium,.e. g.,

.40% chromium, %to 25% silicon, e. g.,

silicon, 5% to 15% manganese, e. g., 12% manganese, 0.2% to 2% calcium,often also containing 0.2%- to 2% titanium, and balance mainly iron wasused instead of the present improved alloys a tensile strength of about65,000 pounds per square inch was obtained but this was accompanied by amuch greater chill depth on a similar test chilled block of about /a2inch. When a 1% late addition of an alloy containing about 92% nickeland 6% silicon was used a tensile strength of about 63,000 pounds persquare inch and a chill depth of about /32 inch was obtained.

When a late addition of ferro-silicon was used a tensile strength of63,000 pounds per square inch and a chill depth of about "/ai inch wascast iron for use in the production of pistons and other'cast ironproducts.

bodies; bushings, grate bars, hardware, plumbing goods, and numerousother cast iron products where machinability, maximum strength, wear 1.An addition alloy for cast iron comprising about 28% to 33% silicon,about 0.3% to 1% calcium, 8% to 12% iron and 58% to 62% nickel, the sumof the silicon, iron and nickel contents being approximately 98% of thealloy.

2. An addition a'lloy for cast iron comprising about 28% to 33% silicon,0.3% to 1% calcium, 8% to 12% iron and the balance substantially allnickel.

3. An addition alloy for cast iron comprising about 27% to 41% silicon,0.1% to 1% calcium,

7% to 15% iron and the balance substantially all nickel.

4. An addition alloy for cast iron comprising about 27% to 41% silicon,0.1% to 1% calcium, 7% to 15% iron and 50% to 65% nickel, the sum of thesilicon, iron and nickel contents being approximately 98% of the alloy.

5. An addition alloy comprising about 27% to 50% silicon, 0.1% to 1%calcium, a small amount up to 20% iron and the balance substan- It isto. be observed that the present invention provides amethod' which isapplicable to the production of gray cast irons in general, i. e., castirons which when solidified contain graphite in any kind of matrix, tocontrol the microstructure of the cast iron and to obtain a structurecontaining randomly distributed graphite and substantially devoid ofareas containing fine dendritic graphite usually associated with .finefree ferrite,'or to obtain wear resistance by increasing the resistanceto scuffing and galling or to decrease the chill without impairing thestrength or to improve machinability by eliminating hard spots, chill,etc. In some cases it has been found that a dendritic structure mayoccur very near the surface of the casting, say within about 0.02 or0.03 inch of the surface, but this portion is so shallow that it isremoved by the conventional machining required to produce the finishedsurface, e.-,g., the surface which it is desired shall exhibit highresistance to scuffing, and high wear resistance, etc. The invention canbe applied to cast iron produced in the cupola, electric furnace or anyother furnace used in the production of cast iron.

Ihe present invention is applicable to the production of gray cast ironproducts requiring good structure control, such as machine tool beds andframes, cylinder blocks, cylinder liners, piston rings for airplaneengines, pistons, high strength gears, crankshafts, camshafts, brake"'drums, clutch plates, exhaust manifolds, connecting rods, valve stemguides, dies, pump and valve pressure tially all nickel.

. 6. As an article of manufacture, an addition alloy for molten castiron made of a nickel alloy containing about 27% to 50% silicon, 67% to34% nickel,- a small amount up to 20 ,5 iron and 0.07% to 1%calcium,said alloy being characterized by a melting point under about19009 F., a high rate of solution in molten cast iron and by thepropertyof being capable of inoculating cast iron to yield a gray cast ironproduct substantially devoid of dendritic graphite. l

7. A method of making cast iron products which comprises establishing amolten bath of cast iron, introducing therein about 0.25% to 5% of analloy comprising about 27% to 41% silicon,

0.1% to 1% calcium, 7% to 15% iron and the balance substantially allnickel, and casting said molten cast iron shortly thereafter.

8. A method of producing cast iron which comprises establishing a moltenbath of cast iron, incorporating in said bath about.0.25% to 5% of anaddition/alloy comprising about 27% to 50% silicon, 0.1% to 1% calcium,a small amount up to 20% iron, and the balance substantially all nickel,and thereafter casting said molten cast iron.

9. A method of controlling the microstructure of cast iron to obtain acast iron having a structure containing randomly distributed graphitewhich comprises establishing a molten bath of --cast iron, incorporatingin said bath a small amount of an alloy containing about 27% to 50%silicon, a small amount up to 20% iron, 0.07% to 1% calcium and thebalance substantially all nickel, and casting the thus-treated moltencast "iron whereby a cast iron product is obtained havingamicrostructure containing randomly distributed graphite andsubstantially devoid of dendritic fine graphite.

10. An addition alloy containing about 27% to iron to yield a gray castiron product substan- 41% silicon, 0.07% to.1% calcium, and 50% to vtially de'void of dendritic graphite. 65% nickel, said alloy beingcharacterized by a I 11. An addition alloy comprising about 27 meltingpoint under about 1900 F., by a high to 50% silicon, 0.1% to 1% calcium,6% to 20% rate of solution in molten cast iron, and by th 5 iron and thebalance substantially all nickel. property of being capable ofinoculating cast JOHN T. EASH.

